feat(notifications): add notification history panel and overlay UX fixes

- New toggleNotificationHistory (Ctrl+N) session-scoped history panel; slides in from same edge as notification stack
- Overlay error/recovery toast follows notifications.overlayPosition; stack and history side seeded at startup
- Cold managed background startup initializes tray and visible overlay shell before tokenization warmups finish
- Add Update button to overlay update-available notifications
- Fix Ctrl+S sentence-card flow: only Anki progress notification, no duplicate status toast
- Fix overlay notification close/actions clickability above subtitle bars on Linux
- Increase pause-until-ready default timeout from 15s to 30s

plugin/subminer/session_bindings.lua

@@ -244,6 +244,8 @@ function M.create(ctx)
 			return { "--toggle-secondary-sub" }
 		elseif action_id == "toggleSubtitleSidebar" then
 			return { "--toggle-subtitle-sidebar" }
+		elseif action_id == "toggleNotificationHistory" then
+			return { "--session-action", '{"actionId":"toggleNotificationHistory"}' }
 		elseif action_id == "markAudioCard" then
 			return { "--mark-audio-card" }
 		elseif action_id == "markWatched" then